Flexible or elastomeric substrates are used in a variety of applications. For example, tapes, bandages, coverings, labels, food packaging and the like are often prepared from flexible or elastomeric substrates. Pressure-sensitive adhesive webs are one example of a flexible or elastomeric substrate that is used to form tapes for joining, mending, masking, sealing, splicing, protecting, reinforcing, identifying and as part of fabrics or for home decorating items. Pressure-sensitive adhesive webs are often employed as coverings for walls, and the like. Flexible or elastomeric substrates are typically prepared from materials such as polyester, polyethylene, polyurethane, polypropylene, nonwoven elastomeric webs, such as those disclosed in U.S. Pat. No. 5,230,701 to Meyer, et al. and ionomers.
In many applications of flexible or elastomeric substrates, it is desirable to have a printed message or design on an exposed surface, generally on the adhesive-free side of the substrate where the substrate comprises a surface having adhesive positioned thereon. Inks typically include hard, waxy components and the integrity of the ink when printed onto a flexible surface, and particularly an elastomeric surface, can therefore be a problem. For example, many inks when printed on a flexible surface shatter or otherwise breakdown and many flexible surfaces do not bind well to the inks. Moreover, maintaining the integrity of the ink when printed onto a porous elastic (such as the substrate taught by Meyer et al. U.S. Pat. No. 5,230,701) or flexible surface such as can be a problem. Many types of inks do not bind well to porous elastic or flexible surfaces. Breakage of the ink resulting from the flexibility of the surface or the porous nature of the surface can reduce the durability of the ink. In addition, when some commonly available inks are used for printing, the inks tend to rub-off either onto an adjoining surface, such as when a flexible or elastomeric substrate is coated with an adhesive and another side is coated with a low adhesion backsizing (LAB) or through rubbing or manipulation of the printed surface, such as can occur with some tapes, such as packaging tapes or bandages.
A common procedure in handling a pressure-sensitive adhesive web is to wind it in a roll with adjacent contact between adhesive-coated and adhesive-free sides with the web being unwound prior to use. In order to facilitate unwinding of this roll, the adhesive-free side of the web is usually coated with an appropriate “low adhesion” or release coating, often termed a low adhesion backsize or LAB. These coatings do not assist in abrasion resistance to a great extent, particularly for applications where the substrate is exposed to extensive abrasion, flexing, elevated temperatures, and the like.
Inks having low rub-off properties are known in the prior art. Attempts have been made to modify ink by the addition of natural or synthetic waxy materials, but these additives tend to migrate into an adhesive when used in a roll of pressure-sensitive adhesive webbing or easily rub-off with mild abrasion. Durability of inks has been manipulated by the addition of waxes or resins. Inks with wax can exhibit improved mar resistance, slip and water repellency properties. Wax of a controlled fine particle size can be mixed or ground into the batch along with pigments or may be introduced during the final blending operations. Alternatively, the wax can be compounded into a “wax media” by dispersing or melting the wax into the varnishes and/or solvents and adding these to the ink.
It is generally known that non-rub qualities imparted by an individual wax are a function of both the particle size and the hardness as well as the melting temperature of a particular wax. However, addition of waxes to inks to impart non-rub qualities to an ink introduces other problems, particularly for printed flexible or elastomeric substrates. For example, with wax, the heat and movement imparted by abrasion on a printed flexible or elastomer surface can result in particles in the film balling up and creating unprinted areas. Increased amount of wax added to improve rub resistance causes problems related to the hardness and the gloss of the printed ink. The addition of wax to ink almost invariably decreases their gloss and a glossy printed image tends to be more visible and therefore, more desirable for many applications. In addition, the use of some waxes, such as microcrystalline or polytetrafluoroethylene waxes are expensive, resulting in increased cost in the production process.
Synthetic waxes such as polyethylene waxes and polytetrafluoroethylene waxes are used in the ink industry. Such waxes are often added as a “non-rub” or a “slip” medium. This medium is generally a fine dispersion of wax in the ink solvent, oil or resin that is compatible with the ink formulation in which it is to be added. Waxes prepared from polytetrafluoroethylene powders can be used in a variety of printing inks, but are particularly useful for heatset inks, where the temperature of the drying apparatus does not cause them to soften or melt. Polytetrafluoroethylene-based waxes can also be stirred into finished inks to improve rub and scuff resistance. Nevertheless, the relative cost of a polytetrafluoroethylene wax is prohibitively high form many applications.
The term “abrasion resistance” can be used in the ink art to refer to the ability of an ink to minimize its damage to the printing plates, such as those used in the gravure printing process. For example, U.S. Pat. No. 5,173,111 to Krishnan et al. discloses an abrasion resistant printing ink that incorporates alkoxylated dibasic phosphate esters and an alkali metal salt of a dialkylsulfosuccinic ester as a method for decreasing wear on printing plates and thereby reducing the need for resurfacing of the plates.
Alternatively, abrasion resistance is also used in the ink art to refer to the ability of an ink composition to resist wear on the printed substrate. For example, U.S. Pat. No. 4,704,163 uses a synthetic polymeric low adhesion backsize compound, such as polyvinyl N-octadecyl carbamate, as an additive to flexographic ink to protect the print on rolled tape from lifting off when the tape is unrolled.
U.S. Pat. No. 4,337,183 to Santiago discloses a printing composition comprising a polyurethane and a polyethylene resin. The polyurethane in this composition functions as a hard resin binder for a lubricity aid. While Santiago indicates that the compositions can be used to print onto metals or plastics, the compositions would not be useful for many flexible substrates and would not be useful on elastomeric substrates.
There remains a need for cost-effective, wear-resistant inks suitable for use on flexible or elastomeric substrates.